Human beings are a punitive species. Perhaps because we are social animals, and require the cooperation of others to achieve our goals, we are strongly disposed to punish those who take advantage of us. Those who ‘free-ride’, taking benefits to which they are not entitled, are subject to exclusion, the imposition of fines or harsher penalties. Wrongdoing arouses strong emotions in us, whether it is done to us, or to others. Our indignation and resentment have fuelled a dizzying variety of punitive practices – ostracism, branding, beheading, quartering, fining, and very many more. The details vary from place to place and time to culture but punishment has been a human universal, because it has been in our evolutionary interests. However, those evolutionary impulses are crude guides to how we should deal with offenders in contemporary society.

Our moral emotions fuel our impulses toward retribution. Retributivists believe that people should be punished because that’s what they deserve. Retributivism is not the only justification for punishment, of course. We also punish to deter others, to prevent the person offending again, and perhaps to rehabilitate the offender. But these consequentialistgrounds alone cannot justify our current system of criminal justice. We want punishments to ‘fit the crime’ – the worse the crime, the worse the punishment – without regard for the evidence of whether it ‘works’, that is, without thinking about punishment in consequentialist terms.

Deterrence works (at least somewhat) for property crimes, but not very well for many different kinds of assault and homicides, and most murderers are very unlikely to reoffend. On purely consequentialist grounds, we probably treat murderers much more harshly than we can justify. And of course, prisons very often make people worse, rather than better. If people didn’t deserve retributivist punishment, we would probably have to incarcerate far fewer people for much shorter periods, in much better conditions.

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So the justification of our current system of punishment depends on whether people deserve harsh treatment. Some thinkers, including Sam Harris and the neuroscientist John-Dylan Haynes, have suggested that, in fact, no one at all deserves to be punished because our choices and behaviour are all determined by physical processes we can’t control. Most philosophers are unconvinced. They are compatibilists: they think that free will and moral responsibility are compatible with determinism. Determinism doesn’t coerce or compel us, and it doesn’t prevent us from assessing reasons and responding appropriately. If anything, determinism enables us to do these things. I think the compatibilists are right: determinism does not undermine our freedom or responsibility. But there are other obstacles to the possession of freedom and responsibility that I think are more serious.

We have a strong sense that people don’t deserve to be punished if they did something bad, but only because of chance or luck. When does luck explain how people act? When more than one option is consistent with their values or their character, then chance features of their internal or external environment (psychologists call these ‘primes’) will influence how they act. Whether someone helps or fails to help is influenced by primes constantly. People are more likely to stop and help someone who dropped something, or give them change, if there are pleasant smells in the environment than if there are not; on the other hand, they are more honest if they think they are being watched, even when merely in the presence of a picture of a pair of eyes. These chance features of our environment make a difference to our behaviour all the time.

Whenever you are strongly tempted to do something wrong (to drive off without leaving a note on the windshield of the car you’ve hit; to keep the wallet that you just saw someone drop), you are probably in a situation in which luck can make a big difference to how you act. A smell, a picture, a sound (which reminds you of your mother, or your boss) can make the difference between doing the right thing or not.

But of course there are lots of situations in which luck doesn’t make this kind of difference. Some people would keep the money without a second thought, or mug a passerby if they thought they could get away with it. Yet most of us would never mug someone, so we’re resistant to that kind of luck. Still, the fact that people are different in the way that they respond to temptations to do wrong is also due to luck – a different kind of luck.

People might be good or bad due to what the philosopher Thomas Nagel in 1979 called constitutive luck. This is luck in one’s genes, or the environment in which you grew up, which leads to someone being a particular kind of person, with a distinct set of strengths, weaknesses, talents and values.

Some philosophers argue that we can take responsibility for our constitutive luck. It’s certainly true that adults are never just the product of their genes and formative environment. Their choices have shaped the kind of people they are. But these choices, too, are shot through with luck. When they are easy choices, they merely express our constitutive luck. To the extent to which they are not easy, they are vulnerable to present luck. Between them, constitutive and present luck seem to strip away all blame and all praise due to us for our actions.

Of course, you might not agree with me that luck plays such an important role in who we are and how we make decisions. But the onus is on those who disagree, not on me. Here’s why: to impose punishments on people is to treat them in a way that is a clear violation of their human rights, if they don’t deserve such treatment. We should refrain from such serious harms unless we have very powerful reasons to think that doing so is strongly justified. Because punishing people involves harming them, we should refrain from retributive punishment unless we have really strong arguments for it.

Does my responsibility-skepticism mean that I believe we should let murderers and rapists go free? Of course not: we have a right and a duty to protect ourselves and others. The other functions of punishment remain legitimate: to deter crime, incapacitate those who can’t be deterred, and rehabilitate offenders.

However, a system of justice that is based on those needs will be very different from present-day systems of retributive punishment, especially prolonged imprisonment. Sometimes there will be an overlap: we will still need to confine some people in places where they can’t re-offend. We won’t get deterrence unless the conditions of confinement are somewhat unpleasant. But for those people who are not psychopaths, confinement could be very short. The data from criminology is messy and hard to interpret, but there are reasons to think that we can secure all the deterrence benefits of prison sentences with very much shorter sentences.

By spending more on rehabilitation, and on policies that ameliorate criminogenic environments, we can ensure that there are fewer people who will choose crime. There will likely remain a class of people who are not deterred, and some of them will be dangerous. They might require longer sentences. But there are likely to be relatively few of them, and the costs of housing them in secure but non-punitive environments need not be high. If we can overcome our evolutionary bent to mete out brutal treatment to those who break the social codes, we begin to glimpse responses to crime that are much less harsh, but much more effective in reducing its costs.